The long term objective is to develop an optical instrument (using fluorescent antibodies) for viral diagnosis that is so sensitive, rapid, simple and inexpensive that it will have wide research and diagnostic usage. The specific aim is to identify (within 10 minutes) a single virus in concentrations down to 10 viruses/mL in raw samples. This will be done in part by measuring the fluorescence from a single fluorescent antibody and simultaneously measuring the light scattering from a single virus to which it may be bound.